Pageable and Discardable Code in a Protocol Driver
Driver developers should designate code as pageable whenever possible, freeing system space for code that must be memory-resident. You can mark functions as pageable with the NDIS_PAGEABLE_FUNCTION macro. The IRQL, resource management features, and other characteristics of a function might prohibit the function from being pageable.
Every ProtocolXxx function runs at an IRQL in the range from PASSIVE_LEVEL to DISPATCH_LEVEL. Functions that run exclusively at IRQL = PASSIVE_LEVEL should be marked as pageable.
A driver function that runs at IRQL = PASSIVE_LEVEL can be made pageable as long as it neither calls nor is called by any function that runs at IRQL >= DISPATCH_LEVEL--such as a function that acquires a spin lock. Acquiring a spin lock causes the IRQL of the acquiring thread to be raised to DISPATCH_LEVEL. A driver function, such as ProtocolBindAdapterEx, that runs at IRQL = PASSIVE_LEVEL must not call any NdisXxx functions that run at IRQL >= DISPATCH_LEVEL if that driver function is marked as pageable code. For more information about the IRQL for each NdisXxx function, see NDIS Library Functions.
The DriverEntry function of NDIS protocol drivers, as well as code that is called only from DriverEntry, should be specified as initialization-only code, by using the NDIS_INIT_FUNCTION macro. Code that is identified with this macro is assumed to run only once at system initialization time, and, as a result, is mapped only during that time. After a function marked as initialization-only returns, it is discarded.